1. Field of the Invention
The present invention relates to a belt skew correcting device used for a belt carrying device including an endless belt, a belt device including the belt skew correcting device, and an image forming apparatus including these devices.
2. Description of the Related Art
Conventionally, an image forming apparatus incorporates various types of endless-shaped belts (hereinafter, referred to as endless belts) as a latent image carrying body, an intermediate transfer body, a recording medium conveying member, an image fixing member, and the like. Such a kind of belt is configured to move in a constant direction while being stretched across at least supporting two rollers.
There is a problem generally called “belt skew” in that an endless belt skews or deviates in a direction orthogonal to the conveyed direction of the endless belt. Such a belt skew is caused for example by a problem in materials of the endless belt or components related thereto, processing accuracy for the endless belt and the components, or aging degradation of the components, and the like. If the belt skew occurs, for example, a positional deviation occurs in an image transferred onto a recording medium such as a recording sheet, or the endless belt comes off from a supporting roller and is broken. Therefore, it is necessary to suppress an occurrence of belt skew and to correct the belt skew if it occurs.
Conventionally, various methods have been proposed in order to suppress or correct, if occurred, the belt skew. For example, Japanese Patent Application Laid-open No. 2006-162659 discloses a configuration of a belt skew correcting mechanism. In this configuration, an endless belt is supported by a plurality of rollers, and one of the rollers (supporting roller) is arranged to be tiltable. For this purpose, a shaft of this supporting roller, which rotatably supports the same, has one end which is tiltably supported with respect to the other end thereof serving as a pivotal point. Between the tiltable end of the roller shaft and the supporting roller, the shaft of the supporting roller (roller shaft) is provided with a following member that follows a movement of the endless belt along the shaft due to the belt skew. Between the tiltable end and the following member, there is provided a displacement member which is configured separately from the following member and which tilts the one end of the roller shaft in accordance with the following movement of the following member along the roller shaft. The following member is a pulley member which engages a bead arranged at one end of the endless belt. And, the following member is rotatable around the roller shaft, and is movable along the roller shaft following to the skew of the endless belt. The dislocating member, to which the shaft of the supporting roller (roller shaft) is inserted, is provided with a plate portion which has an elongate hole for regulating the movement of the inserted roller shaft only in the tilting direction, a projecting portion along which the following member slides, and an engaging portion which engages a pivotal shaft arranged fixedly at the device body. The pivotal shaft arranged fixedly is spaced from the shaft of the supporting roller with a predetermined angle with respect to the shaft of the supporting roller, so that the displacement member can rotate around the pivotal shaft. If the endless belt skews or deviates toward the tiltable end of the roller shaft, the projecting portion of the displacement member is pressed by the following member, and the portion of the roller shaft which is supported by the elongate hole rotates around the pivotal shaft so as to move substantially upward. On the other hand, if the endless belt skews or deviates toward the other end of the roller shaft (the pivotal end of the roller shaft), the portion of the roller shaft which is supported by the elongate hole presses the following member because of the own weight of the supporting roller, and rotates around the pivotal shaft so as to move substantially downward. Since the displacement member rotates (moves pivotally) in accordance with the skew of the endless belt, the roller shaft tilts by an angle in accordance with the skew of the endless belt with respect to the pivotal end thereof. While the endless belt rotates, a force is generated from a friction among the endless belt, the supporting roller and the following member. Due to this force from the friction, the angle of the roller shaft is converged to an angle when the belt skew does not occur, so that the belt skew is corrected. This convergence makes it possible to suppress and correct, if occurs, the belt skew.
Japanese Patent Application Laid-open No. 2009-186910 discloses a configuration of a belt skew correcting mechanism. In this configuration, an endless belt is supported by a plurality of rollers, and one of the rollers (supporting roller) is arranged to be tiltable. For this purpose, a shaft of this supporting roller, which rotatably supports the same, has one end which is tiltably supported with respect to the other end thereof serving as a pivotal point. Between the tiltable end of the roller shaft and the supporting roller, the shaft of the supporting roller (roller shaft) is provided with a following member that follows a movement of the endless belt along the shaft due to the belt skew. At an end of the following member which is an end not facing the supporting roller, there is provided a displacement member which is configured integrally with the following member and which tilts the one end of the roller shaft in accordance with the following movement of the following member along the roller shaft. The following member is a member provided with a cylinder-shaped portion onto which one end of the endless belt is mounted, and a flange portion which abuts on the one end of the endless belt. The following member rotates in accordance with the rotation of the endless belt, and can moves along the roller shaft following to the skew of the endless belt. The displacing member is configured integrally with the following member via a bearing, and is supported movably with respect to the roller shaft along the same. A part of the displacing member is formed to be conical shape having a smaller diameter at the following member side thereof. The displacing member is disposed at a position far from the endless belt than the following member, and is always pressed toward the endless belt by a pressing member. A guide member having a cylindrical shape substantially vertical with respect to the roller shaft and having a substantially horizontal central axis abuts on the conical part of the displacing member from the lower side.
If the endless belt skews or deviates toward the vertically movable end of the roller shaft, the conical part of the displacing member which is integrally with the following member is guided in such a manner that the conical part slides down from the guide member due to the own weight of the supporting roller and the like. Thus, the conical part moves toward vertically movable end of the roller shaft. Since the conical part moves as described above, a vertical position of the roller shaft where the guide member supports the shaft is lowered, so that the supporting roller tilts downward. On the other hand, if the endless belt skews or deviates toward the pivotal end of the roller shaft, the conical part of the displacing member which is integrally with the following member is pressed by the pressing member and guided by the guide member in such a manner that the conical part slides up from the guide member. Thus, the conical part moves toward the pivotal end of the roller shaft. Since the conical part moves as described above, the vertical position of the roller shaft where the guide member supports the shaft is raised, so that the supporting roller tilts upward. Thus, since the displacing member is guided by the guide member in accordance with the skew of the endless belt, the roller shaft tilts with respect to the other end serving as the pivotal point with an angle corresponding to the skew of the endless belt. While the endless belt rotates, a force is generated from a friction among the endless belt, the supporting roller and the following member. Due to this force from the friction, the angle of the roller shaft is converged to an angle when the belt skew does not occur, so that the belt skew is corrected. This convergence makes it possible to suppress and correct, if occurs, the belt skew.
In the configuration disclosed in Japanese Patent Application Laid-open No. 2006-162659, however, a backlash may occur because of uneven abrasion between the roller shaft and an inner peripheral surface of the displacing member which engages the roller shaft, or between the elongate hole which supports the roller shaft and the roller shaft which slidably moves along the elongate hole. If the backlash occurs at these parts, the conversion may become stepwise when the roller shaft converges to a status with no belt skew, or the conversion itself may become impossible. Furthermore, if the status that the roller shaft cannot converge to a status with no belt skew continues for a long time, a positional deviation of a transfer image on a recording medium such as recording paper or the like may occur, or the endless belt may be damaged because of the detachment of the belt from the supporting roller. If the abrasion is advanced at these parts, the normal skew correction is likely to be impossible, and the durability as the belt skew correcting mechanism becomes unsure. Thus, the configuration disclosed by Japanese Patent Application Laid-open No. 2006-162659 still has a problem in the stable belt skew correction and the durability thereof.
On the other hand, in the configuration disclosed by Japanese Patent Application Laid-open No. 2009-186910, the cylinder shaped guide member, of which central axis is substantially horizontal and which is disposed substantially vertical to the roller shaft, abuts on the conical part of the displacing member. Thereby, the abutting position is a point, and the backlash may occur because of uneven abrasion. Therefore, the configuration disclosed by Japanese Patent Application Laid-open No. 2009-186910 still has a problem in the stable belt skew correction and the durability thereof, similarly to Japanese Patent Application Laid-open No. 2006-162659.